SYMPATHETIC SYSTEM IN BIRDS 297 



level. The ganglia of the trunk lie close to the walls of the oesoph- 

 agus just distal to the origin of the trachea. The bifurcation of 

 the trachea occurs farther anteriorly in birds than in mammals, 

 and the bronchi are comparatively longer. Anterior to the bifur- 

 cation of the trachea, cells deviate from the course of the vagi 

 along the fibers of their growing branches and wander into the 

 walls of the oesophagus. These cells are so slightly differentiated 

 at this stage that it is no longer possible to trace them after they 

 have entered the denser tissues of the oesophageal walls. Beyond 

 the bifurcation of the trachea, the vagus trunks bend laterally and 

 ventrally round the bronchi and extend along the ventro-lateral 

 aspects of the oesophagus, continually approaching each other 

 posteriorly. At the point where the vagi begin to bend round the 

 bronchi, each vagus trunk gives rise to a slender branch which 

 extends posteriorly along the wall of the oesophagus between the 

 latter and the bronchus. These branches may be traced poster- 

 iorly but for a short distance at this stage. 



At the close of the sixth day, the vagi have become more con- 

 spicuous. In the anterior region, definite lines of cells may be 

 traced from the vagus trunks into the walls of the oesophagus 

 where they become aggregated into more or less distinct groups 

 arranged in two broken rings (fig. 7, m.s.p.). Posterior to the bi- 

 furcation of the trachea, cells may be traced dorsally from the 

 vagus trunks into the walls of the oesophagus (fig. 9, m.s.p.). 

 The vagus branches lying between the walls of the oesophagus 

 and the bronchi have become more conspicuous and may be traced 

 posteriorly as far as the region of the lungs. Posterior to the region 

 of the heart, the vagus trunks lie close together and apparently 

 break up to form a plexus ventral to the oesophagus. 



During the seventh and the eighth day of incubation, the sym- 

 pathetic plexuses in the walls of the digestive tube become well 

 established. Branches of the vagi may be traced into the walls 

 of the oesophagus, and the cell-groups constituting the anlagen 

 of the myenteric and the submucous plexuses assume a more defi- 

 nite arrangement. 



The sources of the cells giving rise to the myenteric and the 

 submucous plexuses in the walls of the small intestine could not 



THE JOURNAL OF COMPARATIVE NEUROLOGY AND PSYCHOLOGY, VOL. 20, NO. 4. 



